What you're describing suggests a label merge. Label merges use table cells of a fixed height and width to hold and format each record and the format naturally prevents records being split across pages. For a custom set-up you could also format the table to disallow rows breaking across pages.

Similarly, for a directory/catalogue merge, you could separate the lines within each record with line breaks, reserving the use of paragraph breaks for separating the records. The paragraph format would also use the 'keep lines together' attribute.

All this setup would be done once, in the mailmerge main document, so no post-processing would be required.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]